Question: On the first 4 quizzes of her history class, Emily got an average score of 79. What does she need on the next quiz to have an overall average of 83?
Let her score on the next quiz be $x$ The sum of all of her scores is then $4 \cdot 79 + x$ The same sum must also be equal to $5 \cdot 83$ Solve: $x = 5 \cdot 83 - 4 \cdot 79 = 99$.